Comtech EF Data SDM-9000, Installation And Operation Manual

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SDM-9000 Satellite Modem Options
Rev. 4 A–21
A.2.7 Reed-Solomon Coder/Decoder
The Reed-Solomon coder receives scrambled data packets in byte serial format.
RS(204,188,8) shortened code—from the original RS(255,239,8) code—is applied to
each scrambled transport packet (188 bytes) to generate an error-protected packet. Refer
to Figure A-17 for the packet arrangement.
SYNC
BYTE
SCRAMBLED PAYLOAD (187 BYTES)
204 BYTES
(1,632 BITS)
RS(204,188,8)
16 BYTES
Figure A-17.
Reed-
Solomon RS(204,188,8) Error-Protected Packet
Note: RS coding is also applied to the non-inverted or inverted packet sync byte.
The shortened Reed-Solomon code is implemented by adding 51 bytes, all set to zero, to
the information bytes at the input of a (255,239) encoder. These bytes are discarded after
the encoding procedure.
The code and field generator polynomials are shown below.
Code Generator Polynomial:
g(x) = (x +
α 0
) (x +
α 1
) (x +
α 2
)
…
(x +
α 15
)
Field Generator Polynomial:
p(x) = x8 + x4 + x3 + x2 + 1